A lawyer needs to be contacted about this and they can direct you to what is needed. Often a "specific POA" is needed. These are POA but they have verbiage allowing the holder to dispose of property and often a specific property.
I am not an attorney, however, based on my experience, the power of attorney would need to be cleared first by both the title company and lender prior to being ok. Consult with you attorney for the best advice on this as every purchase situation is unique.